What is the kinematic model formula of the four-wheel differential robot

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we want to control the movement of the four wheels of the robot according to the received robot linear and angular velocity, and calculate the current linear and angular velocity of the robot according to the feedback speed of the four wheels. What is the kinematics equation of the four-wheel differential robot? What is the difference with the common two-wheel differential? Thank you!

The picture is my robot. All four wheels can only rotate and cannot change the wheel direction like a car ](https://i.stack.imgur.com/DbXxc.jpg)